Pentafluoroethane (known in the trade under the designation F125) has been proposed as a substitute for chloropentafluoroethane (F115) and for chlorodifluoromethane (F22) for the applications linked with the refrigeration industries; on its own or in combination with other HFAs it is especially advantageous for replacing the refrigerant R502 (azeotropic mixture of F115 and F22) widely employed hitherto for the production of industrial cooling.
F125 can be obtained by hydrogenolysis of F115, as described in patent EP 506 525, or by liquid- or gas-phase fluorination of chlorinated or chlorofluorinated compounds. Among these processes there may be mentioned more particularly those starting from olefins like perchloroethylene with addition of a first molecule of HF and substitution of the other chlorine atoms as described in U.S. Pat. No. 3,755,477; as indicated in patent EP 456 552 it is also possible to start with intermediate fluorination products such as 1,1,1-trifluorodichloroethane (F123) and 1,1,1,2-tetrafluorochloroethane (F124).
These processes, in particular those using elevated temperatures, give rise to olefins which are well known for their toxicity as well as for their reactivity. Even at relatively low concentrations these olefins can, for example, be oxidized in contact with air and result in acidic conversion products making the F125 unsuitable for its commercialization.
After distillation, pentafluoroethane can still contain chlorotrifluoroethylene (F1113) originating from the dechlorohydration of 1,2-dichloro-1,1,2-trifluoroethane (F123a), a normal byproduct of the fluorination of perchloroethylene, or from the dehydrofluorination of chlorotetrafluoroethanes (F124 and F124a). During prolonged storage of F125 and in the presence of traces of air which are normally dissolved in liquid F125, F1113 can be easily oxidized and, in contact with residual moisture, result in the formation of acidic products such as HCl, HF and CF.sub.3 COOH. Furthermore, besides its sensitivity to oxidation, F1113 is well known for its ability to polymerize or copolymerize in the presence of other olefins.